Magnetic displacement sensor systems are a common subsystem in many intrusion systems, and security systems more generally. Most often, these magnetic displacement sensor systems are used to detect whether doors or windows are ajar or secured. More generally, however, magnetic displacement sensor systems can be used in other applications that require proximity and/or end position sensing, or moving part position sensing. In these intrusion/security systems, the magnetic displacement sensor systems are typically monitored by a system control panel via a network. In this way, the control panel can monitor whether doors or windows are ajar, or secured, for example.
The magnetic displacement sensor systems have traditionally included magnets and reed switches. When the magnets, which are usually installed on the moving parts, are brought into proximity of the reed switches, which are usually installed on adjacent portions of stationary parts, the contacts of switches are closed and the switches are conductive. The control panels then monitor the conductivity of the reed switches.
More recently, it has been proposed to use magnetometers in place of the traditional reed switches. The magnetometers detect strength of the magnetic field generated from the magnets. The corresponding magnetic displacement sensors then determine whether the door, for example, is ajar, or not, by determining whether the magnetic field strength detected by the magnetometers are greater or less than a threshold, which is typically established through a calibration step.